Attenuator circuit



Mardi 16 l943- H. M. LEwls 2,313,952

ATTENUATOR CIRCUIT Filed April 7, 1938 2 Sheets-Sheet 1 ATTORNEY INVENTOR March 16, 1943. H. M. LEwls ATTENUATOR CIRCUIT Filed April v. 195s 2 shts-sheec INVENTOR HA OLD M LEWIS ATTORNEY nTl.

Patented Man 16, 1943 FFICE 2,313,952 ATTENUATon cmcm'r nanna M. Lewis, Great Neck, N. Y., assignmto Hazeltlne ware Corporation, a corporation oi' Dela- Appueauon april 7, 193s, seria: No. 200,641

(c1. 25o-2o) 22 Claims.

Iliis invention relates to modulated-carrier signal receivers and, arrangement for reducing the maximum amplitude and the range of amplitude variation of the input to a repeater stage of such a receiver.

Under normal operating conditions, a modulated-carrier signal receiver is subject to the `reception of signals of amplitudes varying within very wide limits. As a result, the input to the first repeater stage of the receiver normally has a correspondingly wide range of variation. For weak signals it is desirable to maintain the gain from the antenna to the rst repeater stage ofthe receiver at a maximum in order to raise the signals substantially above the noise level and thus to procure the maximum useful sensitivity of the receiver. However, as the strength of desired received signals increases to such an extent that the swing of the grid of the rst repeater stage includes a substantial nonlinearportion ofthe characteristic curve lof the repeater, distortion of the desired signal-modulation envelope and cross modulation of the desired carrier by strong undesired signals may result. Thisvis particularly true in the case of receivers provided with automatic ampliilcation control by which strong signals cause'the grid to be biased toward that portion of its char.

acteristic which is most nonlinear. Undesired signals as well as desired signals which reach the input electrodes' ofthe first repeater stage have the effect of increasing the grid swing to such an extent that these disturbing elects result. It is Well known that such envelope distortion and cross modulation are leiects which cannot be filtered out by succeeding selective circuits.

In general, the circuit between the antenna and the input circuit of the rst vacuum-tube repeater-in the signal-translating channel) should be selective topass a band of desired modulation frequencies sufiiciently wide to provide the desired delity of reproduction. Generally speaking, if an attempt is made to decrease the total desired and undesired signal input of the first repeater stage by discriminating against the undesired signals passed by the selector, as by adlusting its band width, the delity of reproduction is impaired to an undesirable degree. Furthermore,

' this does notremove the envelope distortion of abnormally strong signals. n

Various expedients have heretofore been proposed for automatically and adjustably attenuating the input to the first repeater stage of more particularly, to an preselector circuit (the selector a modulated-carrier receiver in order to eliminate the disturbing effects described above. In certain of these arrangements adjustable impedance elements, such as vacuum tube have been connected in circuit with the preselector circuit of the receiver adjustably to damp such circuits, thereby adjustably to attenuate the lnput to the rst repeater. This type-of element, y however, is usually of inherently high impedance which restricts its application to a parallel connection with other elements of the preselector circuit. As thus connected, such an adjustable impedance generally has an undesirable elect on the selectivity or band-pass characteristic of the selector with which it is associated. In addition, both desired and undesired signals may be present with amplitude suiicient to cause nonlinear iiuctuations of the vacuum-tube shunt conductance with resulting envelope distortion of the desired signal and cross modulation thereof by an undesired signal in the 'attenuating tube itself. Furthermore, the interelectrode capacitance of a vacuum tube so connected incidentally inuences the resonant frequency of the circuit with which it is connected. This effect is undesirable in radio-frequency ypreselector circuits which are tunable over a wide range of frequencies, both because it tends to restrict the tuning range and because its detuning'elect may vary with adjustments or its attenuation eiect.

Another circuit which is not subject to the disadvantages of that just mentioned is described in Athe copending application of Harold A. Wheeler, SerialNo. 149,795, led June 23, 1937, new United States Patent No.2,182,329, and assigned to the same assigneel as the present invention. The arrangement of the copending Wheeler application, however, utilizes temperature variable resistances in the pre-attenuator circuit, thus adding to the complexity and the expense ofthe receiver. Still another circuit vnot subject to the disadvantages mentioned above is described in the copending applicationl of Daniel E. Harnett and John F. Farrington, Serial No. 200,610, iled concurrently with the present application, now United States Patent No. 2,204,216, and also assigned to the same assignee as the present application. Brleiy, the arrangement of the Harnett and Farrington application comprises two coupling paths between the antenna and `the rst vacuum-tube repeater of the signal channel of the receiver. One of these coupling paths is of the conventional type and the other comprises a vacuum-tube signal repeater, the transconductance of which is varied in accordance with the intensity of received sig'- nals. The two coupling paths are oppositely phased sothat they opposition in the input circuit of the first vacuum-tube repeater of the signal channel of the receiver.

It is an object of the provide an improved, simple, and economical attenuator which may be easily adjusted to control the sensitivity of a modulated-carrier signal receiver in such manner as to eliminate the undesired effects described above.

'It is a further object of the invention to provide an attenuator for adjustably attenuating the input to the first repeater'stage of a modulated-carrier signal receiver with freedom from undesired cross modulation of the desired signal carrier by strong undesired signals on nearby frequencies.

It is a further object of the invention to provide a preattenuator of the type described which secures the desired result without affecting the selectivity of the radio-frequency selector with which it is associated.

Brieiiy, the above objects are obtained in accordance withv one embodiment of the present invention by providing a preattenuator comprising two coupling paths between the antenna andthe iirst vacuum-tube repeater of the signaltranslating channel of a modulated-carrier signal receiver, the coupling paths being so arranged as to supply signal voltages of opposite phase to the input circuit of the repeater. One of these coupling paths provides a fixed normal coupling between the antenna and the repeater,

. while the other path comprises means whereby its transmissionv efliciency is controlled to vary its effectiveness. When the transmission eiliciency of the second coupling path is very small, normal antenna coupling is obtained through the first fixed coupling path. However, when the transmission efficiency of the second coupling path is increased, a`substantial voltage approximately in phase opposition to the voltage coupled to the input of the first repeater tube through the normal coupling path is developed in the input circuit of the first repeater through the second or auxiliary coupling path. The output circuit of the second or auxiliary coupling path is connected across a cathode resistor in the input circuit of the first repeater of the signaltranslating channel. In one 4embodiment of the invention, this resistor forms substantially the total load impedance of a signal repeater or control tubeincluded in the second coupling path. As thus connected, the resistor is also effectively a cathode-biasing resistor for both the control tube and the first repeater tube. Variation of the bias voltage applied to the control tube is used to regulate the signal voltage applied to the input circuit of the first repeater through the auxiliary coupling path, thereby reducing the total effective coupling between the antenna and the input circuit of the first repeater stage of the receiver and limiting the resultant voltage applied to the input circuit of the first tube.

In another embodiment of the invention, an

f attenuator similar in many respects to the embodiment described above is procured by utilizing a single vacuum tube having certain electrodes which are common to the two coupling paths. In this embodiment of the invention, the tube may be of the conventional pentode type, the normal coupling path being connected develop voltages in phasev invention, therefore, to i to its-signal input circuit so that it constitutes the first radio-frequency amplifier of the receiver having an unby-passed cathode resistor, but having its anode circuit returned directly to the cathode for radio-frequency currents. In this embodiment of the invention, the auxiliary or control coupling path, for developing an opposing signal voltage across the cathode resistor of the tube,fis provided by the screen-grid'circult of the pentode tube. The transmission eiliciency of the tube with respect to the anode and screen-grid circuits is controlled in opposite senses by a potential varying in accordance with the amplitude of received signals which is applied to the suppressor grid.

In. accordance with another embodiment of the invention, there is provided in combination with a tube including at least a cathode, a signal input electrode and an output electrode, a signal input circuit which is coupled to the input electrode, and a signal output circuit which is connected to the output electrode. There is also provided a means responsive to electrons diverted from the electron stream flowing between cathode and output electrode for developing a signal voltage. In addition there is provided means for applying the developed signal voltage to the input electrode in degenerative phase relative to the signal voltage from the input circuit, and a single means for simultaneously controlling the magnitude of the electron diversion and the intensity of the electron stream to the output electrode.

The novel features which are believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of op-eration, together with further objects thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings, in which Figs. 1, 2, and 3 are circuit diagrams, partially schematic, of different forms of the attenuator system as embodied in a broadcast receiver of the superheterodyne type.

Referring to Fig. 1 of the drawings, there is shown a circuit diagram, partially schematic, of a complete modulated-carrier signal receiver of the superheterodyne type employing the invention. This receiver comprises, in cascade in the signal-translating channel thereof, a receiver input or antenna-ground circuit I0, II, a` preattenuating circuit I2, a vacuum-tube radio-frequency amplifier I3 including an input circuit, a frequency changer or oscillator-modulator I4, an intermediate-frequency amplifier I5 of one or more stages, a detector and automatic amplification control or A. V. C. supply I6, an audio-frequency amplifier I1 of one or more stages, and a sound reproducer I8. The attenuator I2 comprises a coupling circuit for coupling the input circuit of the receiver to the input circuit of vacuum tube I3, which coupling circuit will be subsequently described more fully. Automatic amplification control is secured in a well-known manner by applying a unidirectional voltage derived from the A. V. C. supply I6 over conductor I9 to the control electrodes of oscillator-modulator I4 and of one or mor.l of the tubes included in the intermediate-frequency amplifier I5. Suitable operating potentials are supplied to the tubes of the receiver from sources indicated as +B and -i-Sc.

Neglectng for the present the operation of the preattenuator of the invention, the apparatus I ner I3 opposite in phase to the directly tothe input circuit of ampliiier I3 by.v

described constitutes, in general, a conventional superheterodyne radio receiverV having a plurality o! signal selector circuits, the operation of which is weil understood In the art. In brief, signals intercepted by antenna-ground circuit III, II are translated by the selector circuit I2 to the input circuit of radio-frequency amplifier I3, are lamchannel oi' the receiver through condenser 28, while its output circuit is coupledthrough transformer 30, 3| to the diode rectifier 23. Rectifier pliiied therein and translated to oscillator-modulator I4 wherein they are converted to an intermediate-frequency signal. The intermediatefrequency Signal is amplified in intermediate-frelquency ampliiier I5 and delivered to detector I8,

wherein the audio-frequency signals and the A. V. C. biasingV potentials are derived. The

audio-frequency signals are, in turn, amplified by audio-frequency ampliier I1 and supplied to 23 is provided with a load circuit comprising resistor 32,by-passed for alternating currents by condenser 33, across whichthere is developed a unidirectional voltage which varies in magnitude in accordance with the amplitude o'f the signal input toampliner 28. 'I'his voltageis applied positively, lthrough a filter comprising series resisters 34 and shunt condenser 35, to the grid of control tube 25, this. bias voltage, together with that o1 a bias source 32', serving to vary its transconductance. Al cathode-biasing circuit '38 lsound reproducer I8 i'orreproduction. The autois provided for ampliiler 28. To provide an automatic ampliiication control bias for radio-frequency amplifier I3 which is responsive to ,fboth desired and undesired received signals, there'is provided an auxiliary diode anode 31 in ampliiier 2 8 having coupled to its output circuit a load resistor 38v across which the control-.bias voltage yis developed. This voltage is applied negatively III, II and the input circuitto amplifier I3.- This iirst circuit includes a tunedcircuit comprising an inductance 20 anda-condenserfZI, inductance 2 8 being inductively coupled to inductance 22 in the antenna-ground circuit i0, II.- 'I'he low potential terminal of selector e circuit 20, 2I- is grounded for carrier-frequency currents through a condenser 23, while the cathode oi' tube I3 is connected to ground through an unby-passed cathode resistor 24. The preattenuator also includes an auxiliary or second coupling circuit bethrough a circuit comprising a resistor 33 to the control grid of radio-frequency ampliiler I3. In

order ,'to neutralize undesirable capacitive coupling eilects through the grid-cathode capacitance, a voltage is coupled from a winding 40,

which is enectively an extension of winding 20 and coupled thereto, through a neutralizing condenser 4I to the cathode of amplifier I3.

It will be noted that the input circuit of the vacuum-tube repeater 25, and .also that of the auxiliary amplifier 28, comprises simply a resistor which, of course, is aperiodic or nonfrequencyselective. Consequently, it may -be said that the repeater 25 and amplifier '/28 are both nonirequency-'selective and' that their input circuits are simply coupled through the coupling condenser tween the antenna-ground circuit I0, II and the input circuit of amplifier I3 in parallel with the normal coupling circuit and comprising a control tube or vacuum-tube signal repeater 25 having its input circuit for' signal energy connected across selector 20, 2l through a condenser 2B, its cath- 0de being connected to the cathode oi.' tube I3 and to ground through the cathode-biasing resistor 24. In other words, the output circuit of control tube 25 is coupled across resistor 24 which comprises the major part of the load (impedance of this tube. As so connected, the coupling oi' the auxiliary or second coupling path comprising control tube 25 is such as to develop a potential across resistor 24 in the input circuit of amplipotential coupled the normal coupling .path comprising the selector circuit 20, 2|. qnency amspliiier I3 is coupled to the input circuit of oscillator-modulator I4 and returned directly to its cathode for signal-frequency components through a circuit comprising condenser 121 which eil'ectively by-passes resistor 24 in the output circuit of ampliiier I3 for carrier-frequency curwhich varies in accordance with received signal intensities, there is provided an auxiliary amplitying and rectiiying channel including vacuum tubes 28 and 23. The input circuit of auxiliary amplier 28 is coupled to the radio-frequency 'I'he anode circuit oi' radio-fre- 26 to the input circuit or antenna-ground circuit III, II of the receiver. It follows, therefore, that they second coupling circuit 'comprising vacuum tubes 25, 28 and 29 is also substantially nonfrequency-selective. I

, In considering theoperation of the system just described, it will be assumed that, in the absence oi' received signals or for signals ofva very low amplitude, tube 25 is biased to a low value of transconductance or beyond cutoff, so that `:the auxiliary or second coupling circuit of the invention is practically inoperative, the entire coupling between the antenna-ground circuit I0, I I and the input electrodes of radio-frequency amplifier I3 being that Aof,the first or normal coupling circuit comprising selector circuit 20, 2I. Under such conditions, the receiver operates in a conventional' manner. However, as the amplitude of received signals increases, there is an appreciable signal input to amplifier 28 through condenser 28. The l output voltage of amplifier 28 is rectied by diode rents. A decoupling resistor 9 is provided vin the l' Vanode circuit oi' tube I3 and a decoupling circuit rectifier 29 to develop a bias potential across load resistor 32 which varies in accordance with the .amplitude of received signals. This volta-ge is applied positively through the filter 34, 35, 34 to the grid of control tube 25 to increase its transconductance. -Inasmuch as the signal input to tube I3 through the normal coupling path is in phase opposition to that developed across resistor 24, also in the input circuit to tube I3, by the tube 25 in the auxiliary coupling circuit, an increase in the transconductance of the tube 25 serves to ldecrease the resultant effective coupling between the antenna-ground circuit III, I I and the input circuit of vacuum tube I3; that is, to attenuate the signal input to the rst repeaterof the receiver. It will be noted that the resistor 24 received signals.

is effectively an unby-passed degenerative cathod: resistor ior only tube 25. It will be understood that the selective circuits of the receiver following selector circuit 20, 2| are more frequency selective than selector circuit 20, 2I so that the major portion of the selectivity of the receiver is provided by the circuits in the signal-translating channel succeeding the point to which the attenutation control circuit is coupled. Hence, undesired signals as well as desired signals are included in the input to ampliiier 28 so that there may be derived a bias potential which varies in accordance with the amplitude of these` signals. A neutralizing voltage from winding 40 coupled through condenser 4I to the cathode of tube I3 'serves to eliminate undesirable capacitive coupling through the grid-cathode capacitance of the tube. It will be understood that a. iilter circuit, or other circuit having a' resistive impedance over the band of frequencies for which the circuit is to operate, can be utilized in place of resistor 24.

The embodiment of the invention illustrated in Fig. 2 is similar in many respects to that shown in Fig. 1 and similar elements in the two flgures have been given identical reference numerals. The control tube 25 of Fig. 2 is coupled between the antenna-ground circuit I', Il and the input circuit of radio-frequency amplifier I3 is coupled in the same manner as in Fig. l, the difference between the two embodiments being in the source of control bias provided for the control tube 25. In order to provide a control bias for tube 25 of Fig. 2, there is coupled to the output circuit of the control tube through a condenser 50, a rectifier I having a load resistor 52, by-passed for highfrequency currents by a condenser 53, in series with an inductance 54. 'I'he unidirectional potential developed across resistor 52 is applied positively through a resistor 56 to the control electrode of tube 25. A battery 51 provides an initial negative to bias bias tube 25 to cut off in the absence of received signals. In the embodiment of Fig. 2, radio-frequency amplifier I3 is provided with an automatic volume control potential derived from A. V. C. supply I6 through a filter comprising a series resistor 58 and a shunt condenser 59 in a conventional manner.

It will be seen that the operation of the circuit of Fig. 2 is essentially the Same as that of the circuit of Fig. 1, the control tube 25 providing potentials across resistor 24 opposite in phase to those of the normal coupling circuit between the antenna and radio-frequency amplifier I3 in each case. The rectifier 5I coupled to the output circuit ol control tube 25 provides a bias potential for control tube 25, thereby to increase its transof the conventional pentode type which includes a main anode, a cathode, an auxiliary anode or screen grid, an input electrode or signal grid and a suppressor electrode here used as a control grid.

conductance in accordance with the amplitude of It will be seen that the automatic volume control of radio-frequency ampliiier I3 in Fig. 2 is responsive only to desired received signals. It will also be seen that the embodiment disclosed in Fig. 2 provides the required control-bias potentials for tubes I3 and 25 wit-hout the use of an ampliiier tube corresponding to tube 28 of Fig. l. i c

The embodiment of the invention shown in Fig. 3 utilizes only one vacuum tube to provide both the normal coupling path from the antennaground circuit I0, II and the auxiliary coupling path for -developing signal voltages across cathode-biasing resistor 24 opposite in phase to those impressed on the signal-input grid through the normal coupling path. In the embodimentshown in Fig.` 3, this dual purpose tube is shown as radio-frequency amplifier I3, which may be a tube The control electrode last mentioned is disposed between the main anode and the auxiliary electrode which is normally the screen grid of the tube. In order to control the transmission eflciency of the circuits associated with radio-frequency amplifier I3, there is provided an ampliiler 60 having an input electrode coupled across selector 20, 2l through condenser 6I. A gridleak resistor 62 and a cathode-biasing resistor 63, by-passed for alternating currents by a condenser 84, are provided for amplifier 6I). The output circuit ofamplifier l6l) is coupled through a transformer 65, 66 to a diode' detector B1 having a load circuit comprising a resistor 68, by-passed for alternating currents bya condenser 69. The voltagev developed across resistor 681s applied negatively to the normal suppressor grid of radio- Irequency amplifier tube I3.

In considering the operation of the circuit of Fig. 3, it will be seen that the signal-input grid of radio-frequency amplifier I3 controls the cathode emission of the tube and, in the absence of received signals of an appreciable magnitude to provide a bias for the suppressor grid, the received signals are amplified and delivered to oscillatormodulator I4 in a conventional manner. However, as signals of increasing intensity are rcceived, the voltage developed across resistor 68 and applied negatively to the suppressor grid effectively reduces the amplitude of the signal input to oscillator-modulator I4 and increases the signal component of the auxiliary electrode or screen-grid current. The increase in this signalfrequency screen-grid current effectively develops Aa degenerative signal voltage across the resistor 24 which is in the output circuit of the auxiliary electrode that is, a signal-input voltage to tube I3 is developed which is opposite in phase to 'that of the signal voltage due to the normal coupling circuit, thereby attenuating the resultant signal input to radio-frequency amplifier I3 to prevent distortion. and the normal suppressor grid of the vacuum tube I3 act as an automatic volume control source and are, therefore, included in a means for varying the transconductance to the auxiliary electrode of vacuum tube I3 in accordance with the intensity of the received signals. This means is, therefore, responsive to received signals for varying the transconductance from the input electrode to the anode in one sense and the transconductance from the input electrode to the auxiliary electrode or anode in an opposite sense. The suppressor grid and the diode detector 6'I are, therefore, included in a means for simultaneously controlling the electron flow to the output electrode or anode of tube I3 and regulating the electron current flow to the auxiliary electrod-e thereby to control the magnitude of the degenerative voltage. The diode detector arrangement is a single means for simultaneously controlling the magnitude of the electron diversion and the intensity of the electron stream to the output electrode or anode of tube I3.

It will be understood that each of the embodiments of the invention described above can be utilized with any suitable control circuit such as one whichv is responsive to either or both of desired'and undesired received signals.

While there have been described what are at present considered the preferred embodiments of The amplifier 60, the detector 61,

the invention, it will be obvious to those skilled in the art that various changes and modiiications may be made therein without departing from the invention, and it is, therefore, aimed in the apy pended claims to cover all such changes and modiiications as fall within the true spirit and scoren! the invention.

What is claimed is: 1. In a modulated-carrier signal receiver com prising an input circuit and avacuum tube having an input circuit in the signal-translating channel of the receiver, an attenuator comprisinga coupling circuit for coupling said input circuit of said receiver to said input circuit of said vacuum tube, a cathode resistor for said vacuum tube, said vacuum tube having an output circuit returned for signal-frequency components dircctly to its cathode, 'substantially nonirequencyselective means lfor developing across said renistor potentials opposite in phase to those developed in said vacuum-tube input circuit by said coupling circuit, and means for varying the effectiveness of said last-named means to vary the intensity of the signal developed in said output'l circult. y

4 2. In a modulated-carrier signal receiver comprising an input circuit and a vacuum tube ,having an input circuit in the signal-translating channel of the receiver, an attenuator comprising a first coupling circuit for coupling said input circuit of said receiver to said input circuit of said vacuum tube, a cathode-biasing resistor for said vacuum tube, said vacuum tube having an output circuit returned for signal-frequency components directly to its cathode, a second coupling circuit coupled to said input circuit of said receiver and having an output circuit including said resistor,said second coupling circuit developing signal potentials across said resistor opposite in phase to those developed in said vacuumtube input circuit by said iirst coupling circuit, and means for varying the transmission eiliciency of said second coupling circuit to vary the intensity of the signal developed in said output circuit."

3. In a modulated-carrier signal receiver comprising an input circuit, a vacuum tube having circuits' in the signal-translating channel of said receiver, a rst coupling circuit comprising one of said signal selector circuits for coupling said input circuit of said receiver to said input circuit of said vacuum tube, said one of saidselector circuits being less frequency-selective than others of said selector circuits, a cathode-biasing reslstor for said tube, said vacuum tube having an output circuit returned for signal-frequency components directlyr toits cathode, a second coupling circuit having an output circuit including said resistor and developing potentials across said resistor opposite in phase to those developed in said vacuum-tube input circuit by said ilrst coupling circuit, said second couplingcircuit being 'substantially' nonfrequency-selective, a'nd means for controlling the transmission efficiency oi' said second coupling circuit in accordance with the amplitude of received signals.

4. In a modulated-carrier signal receiver tunable over a wide range of signal frequencies comprising an input circuit and a vacuum tube having an input 'circuit in the signal-translating channel of said reeciver, a iirst coupling circuit ior coupling said input circuit of said receiver to said input circuit of said vacuum tubefa cathan inputcircuit, and a plurality oi signal selector resistor comprising substantially the entire load tube having an output circuit returned for signal-frequency components directly to its cathode, a second coupling circuit having an output circuit including said resistor, said second coupling circuit being substantially nonfrequencyselectlve'over said range and Vbeing poled to provide a coupling of opposite phase to that of said first coupling circuit in the input circuit of said vacuum tube, and means for controlling the transmission emciency of said second coupling circuit to vary the intensity of the signal developed in said output circuit 5. In a modulated-carrier signalreceiver comprising an input circuit and a vacuum tube having an input circuit inthe signal-translating rchannel of the receiver, an attenuator comprising a iirst couplingcircuit for coupling said input circuit of said receiver to said -input circuit oi said vacuum tube, a cathode resistor for said tube, said vacuum tube having an output circuit returned for signal-frequency components di-A rectly to its cathode, a second coupling circuit having an output circuit including said resistor and developing potentials across said resistor opposite in phase to those developed in said vacu'um-tube input circuit by said first coupling circuit, an auxiliarybamplifler coupled to said input circuit of said tube, rectifying means coupled to said amplifier for deriving a bias potential varying in accordance with the amplitude of the desired and undesired signal input to said tube.

and means for utilizing saidv bias potential to` .repeater coupled between said input circuit of said receiver and said input circuit of said tube, said vacuum-tube repeater having an output circuit including said resistor, and means for controlling the transconductance of said repeater to vary the intensity of the signal developed in said output circuit.

'1. In a modulated-carrier signal receiver comprising'an input circuit and a. vacuum tube having an input circuit i-n the signal-translating channel of the receiver, an attenuator comprising a ilrst coupling circuit for coupling said input 'circuit of said receiver to said input circuit of said vacuum tube, a second coupling circuit comprising a vacuum-tube' signal repeater coupled between said input circuit of said receiver and said input circuit of said tube, a common cathode-biasing resistor for said tube and said vacnum-tube signal repeater, said vacuum tube'having an output circuit returned for signal-frequency components directly to its cathode, said impedance of said vacuum-tube signal repeater, and means for controlling of said repeater to vary ythe intensity nal developed in said output circuit. y

8. In a modulated-carrier signal receiver comof the sigprising an input circuit, a plurality of vacuum y ode-biasing resistor for said tube, said vacuum 76 tubes having input circuits, and a plurality of signal selector circuits in the signal-translating the transconductance.

:returned channel of said receiver, a first coupling circuit comprising one of said signal selector circuits for coupling said input circuitl of said receiver to said input circuit of one of said vacuum tubes,

said one of said selectors being less frequencyselective than others of said selectors, a second coupling circuit comprising a vacuum-tube signal repeater coupled between said input circuit of said receiver and said input circuit of said one of said tubes, a cathode-biasing resistor for said one oi said tubes, said one of said vacuum tubes havingan'output circuit returned for signal irequencies directly to its cathode, said vacuumtube repeater havingY an output circuit including said resistor, said second coupling circuit being substantially nonfrequency-selective, and means for controlling the transconductance of said repeater to vary the intensity of the signal developed in said output circuit.

9. In a modulated-carrier signal receiver comprising an input circuit and a vacuum tube having an input circuit in the signal-translating channel of the receiver, an attenuator comprising a first coupling circuit for coupling said input circuit of said receiver to said input circuit of said vacuum tube, a cathode-resistor for said tube, said vacuum tube having an output circuit returned for signal-frequency ycomponents directly to its cathode, a second coupling circuit comprisingy a vacuum-tube signal repeater coupled between the said input circuit of said receiver and said input circuit of said tube, said vacuum-tube repeater having an output circuit including said resistor, rectiiying means coupled to the output circuit of said vacuum-tube repeater for deriving a bias potential varying in accordance with the amplitude of the desired and undesired signal input to said'ione of said tube, and means for utilizing said bias potential to control the transconductance of said vacuumtube signal repeater.

10. In a modulated-carrier signal receiver comprising an input circuit and a vacuum tube having an input circuit in the signal-translating channel o! the receiver, an attenuator comprising a first coupling circuit for coupling said input circuit of said receiver to said input circuit of said vacuum tube, a cathode-resistor forl said tube, said vacuum tube having an output circuit returned for signal-frequency components directly to its cathode, arsecond coupling circuit comprising a-'vacuum-tube signal repeater coupled between said input circuit of said receiver and said `input circuit of said tube, said vacuumtube signal repeater having an output circuit including said resistor, means responsive to the input to saidone of said tubes for developing bias potentials varying in accordance with the amplitude of the input to said tubes, means for applying one of said potentials positively to said vacum-tube repeater to vary its transconductance, and means for applying one ci said potentials negatively to said ilrst-named vacumu tube as an automatic amplication control bias.

11. In a modulated-carrier signal receiver comprising an antenna circuit and a vacuum tube having an input circuit inthe signal-translating Vcriminele! the receiver, an attenuator comprisa.: coupling circuit -for coupling said input circuito; ysaid receivexljtol said input circuit of said vacuumtube, lajcitho'de'-bi'asing resistor for said tub e,'said'vacuux`n tube having an output circuit for signal-frequency components diretiy to its cathodefan auxiliary electrode in tively including said resistor for signal-frequency currents, whereby there is developed across said resistor signal potentials opposite in phase to those developed in said vacuum-tube input circuit by said coupling circuit, and means for varying the transconductance of said auxiliary electrode with respect to said vacuum-tube input circuit in accordance with the intensity of received signals.

12. In a modulated-carrier signal receiver comprising an input circuit and a vacuum tube having an input circuit in the signal-translating channel of the receiver, an attenuator comprising a coupling circuit for coupling said input circuit of said receiver to said input lcircuit of said vacuum tube, said'vacuum tube comprising a main anode, an input electrode, and an auxiliary electrode, a cathode-biasing resistor for said vacuum tube, said vacuum tube having an output circuit returned for signal-frequency components directly to its cathode, said auxiliary electrode having an output circuit effectively including said resistor for signal-frequency currents, whereby there is developed across said resistor signal potentials opposite in phase to those developed in said vacuum-tube input circuit by said coupling circuit, and means responsive to received signals Vfor varying the transconductance from said input electrode to said anode in one sense and the transconductance from said input electrode to said auxiliary electrode in an opposite sense.

13. In a modulated-carrier signal receiver comprising an antenna circuit, a vacuum tube having an input circuit, and an automatic volume control source, an attenuator comprising a coupling circuit for coupling said antenna circuit to said input circuit of said vacuum tube, said vacuum tube comprising an anode, an input electrode, and an auxiliary electrode, a cathodebiasing resistor for said vacuum tube, said vacuum tube having an output circuit returned for signal-frequency components directly to its cathode, said auxiliary electrode having an output circuit eiectively including said resistor for signal-frequency currents, whereby there is developed across 4said resistor signal potentials opposite in phase to those of saidcoupling circuit, and means responsive to said automatic volume control source for varying the transconductance from said input electrode to said anode in one sense and the transconductance from said input electrode to said auxiliary electrode in the opposite sense.

14. In a modulated-carrier signal receiver comprising an input circuit and a vacuum tube having an input circuit in the signal-translating channel of the receiver, an attenuator comprising a coupling circuit for coupling said input circuit of said receiver to said input circuit of said vacuum tube, said vacuum tube comprising a signal grid, a control grid, an anode and an auxiliary electrode, said control grid being disposed between said anode and said auxiliary electrode, a cathode-biasing resistor for said tube, said vacuum tube having an output circuit returned for signal-frequency components directly to its cathode, said auxiliary electrode having an output circuit eil'ectively including said resistor for sigsaid vacuum tubehaving an output circuit errecnal-frequency currents, whereby there is developed across said resistor signal potentials opposite in phase to those developed in said vacuumtube input circuit bysaid coupling circuit, and means responsive to the amplitude of received -signals for applying a potential to said control electrode to vary the transconductance from said signal grid to said anode in one sense and the transconductance from said signal grid to said auxiliary electrode in the opposite sense.

15. In a radio receiver, a signal transmission tube including atleast a control grid, a cathode and an output electrode, an impedance connected between-tbe tube cathode and ground, means for applying Signal energy between the tube control.

grid and ground, asignal ,output circuit. connected directly between the control grid and' cathode of said tube, and means for applying a v variable unidirectional voltage to said control grid, thereby to vary the signal output voltage amplitude between said control grid and cathode.

16. In a radio receiver, a signal transmissiontube, mea-ns for applying signal energy between the control grid and cathode of .the tube, an output ,circuit connected directly between the control grid and cathode of the tube, an impedance disposed in the space current path of said tube, means connecting said control grid and cathode of said tube across points of said impedance such that the signal voltage developed across the impedance is applied in degenerative phase between the two electrodes, and means for varying the gal-n of said tube thereby to vary. the signal voltage amplitude delivered to said output circuit.

17. In an amplier of the type including aQ tube provided with at least an electron emission source, an input electrode and anoutput electrode; the method including impressing waves upon said input electrode, developing amplified wave voltage at said output electrode, diverting electrons iiowing from said source to said output electrode, deriving from the diverted electron ilow a wave voltage, combining the derived wave voltage and impressed waves in phase opposition, and concurrently regulating the relative amplitudes of said derived voltage and ampliiled voltage in opposed senses.

18. In a signal transmission network provided with a tube having an electron emission source, an input electrode, an output electrode, and an auxiliary electrode; the method which includes establishing said input electrode at a negative potential relation to said emission source, impressing signals upon said input electrode, deriving at said output electrode amplified signals, deriving a signal voltage from electron ow to said auxiliary electrode, impressing said derived signal voltage upon the input electrode, and controlling the distribution of electrons from said source between said output electrode and said auxiliary electrode.

' 19. In a signal ampliiler, a tube provided with a cathode, a negative signal grid, an output electrode and a positive auxiliary electrode arranged to receive electrons from said cathode, a signal source coupled. between the cathode and signal grid, means operatively associated with the auxiliary electrode to develop signal voltage and impress it indegenerative phase upon said signal grid, anoutput circuit connected to said output electrode, and means for simultaneously controlling the electron flow to said output electrode and regulating the electron current iiow to said auxiliary electrode thereby to control the magnitude'oi said degenerative voltage. l

20. In a signal amplier, a tube provided with a cathode, a signal grid, an output electrode and an auxiliary electrode arranged to receive electrons from said cathode, a control electrode disposed in said tube between said output electrode and auxiliary electrode, a signal source coupled between the cathode and signal grid, means operatively associated with the auxiliary electrode to develop signal voltage and impress it in degenerative phase uponsaid signal grid, an output circuit connected to said output electrode, and means including said control electrode for regulating the electron current iiow to said auxiliary electrode thereby to control the magnitude of said degenerative voltage.

21. In a signal amplifier, a tube provided with a cathode, a negative signal grid/an output electrodeand a positive auxiliary electrode arranged to receive electrons from said cathode, a signal source coupled between the cathode and signal grid, means operatively associated with the auxiliary electrode to developtsignal voltage and impress it in degenerative phase upon said signal grid, an output circuit connected to said output electrode, and means for simultaneously controlling the electron iiow to said output electrode and regulating the electron current iiow to said auxiliary electrode thereby to control the magnitude of said degenerative voltage, said first named means including an impedance connected between said auxiliary electrode and the cathode, and a path of low impedance to signal voltage connecting the signal grid to a point on said impedance.

22. In combination with a tube provided with at least a cathode, signal input electrode and output electrode, a signal input circult coupled to the input electrode, a signal output circuit connectedto the output electrode, means, responsive to electrons diverted from the electron stream no wing between cathode and output electrode, for developing signal voltage, means applying the developed signal voltage to said input electrode in degenerative phase relative to the signal voltage from said input circuit, and a single means for simultaneously controlling the magnitude of said electron diversion and the in tensity of the electron stream to said output electrode.

CERTIFICATE OF CORRECTION.. Patent No. 2,515,952.A i March 16, 19115.

' HAROLD M. mls.

It is hereby certified that error appears in the printed specification of the abovenumbered patent requiring correction as follows: Page 14., first 001mm, une L11, for the words "to bias bias" read --bias to maan; and

second colu'mn, line 11.1, afterf'electrode" insert a semicolon; page 6, first column, lines 58 and 57, claims Sand l0 respectively, strike out "'one of -v sairr; line 65, claim 1o, for "vacuum" read --vacuum; and that the said Letters Patent should be read 'with this correction therein that the same msy conform to the record of the case in the Patent Office. i

lsignaal and seeded this 11th day of may, A. D. 19115.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

